The present invention relates to electrically operated valves and particularly to such valves employed in low voltage operation as, for example, the 12 volt supply employed in on-board motor vehicle applications. More particularly, the invention relates to solenoid operated valves employed in controlling fuel tank vapor emission in motor vehicles and in such applications where it is required to provide the diagnostic leak test of the vapor emission control system. Present systems of this type commonly employ a canister filled with adsorbent such as granulated carbonaceous material for storing fuel vapor during engine shutdown.
Recent legislation has mandated on-board leak testing of fuel vapor emission control systems and this has resulted in the requirement to close the atmospheric air inlet to the fuel vapor storage device or charcoal canister during the leak test cycle. Typically, in motor vehicles having such a canister, an electrically operated valve is employed to control the flow of fuel vapor from the canister to the engine air inlet during engine operation, which flow control is particularly critical during engine idle.
In order to comply with requirements for on-board leak detection diagnostic systems, it has been proposed to measure the flow rate of vapor when the vapor pressure in the tank is equal to the atmospheric pressure or in other words the xcex94P across the tank wall is zero and compare with a flow measurement taken when a vacuum is pulled upon the tank with the canister vent valve closed. An example of such a known system for on-board leak detection of the fuel vapor emission control system is that shown and described in U.S. Pat. No. 5,637,788 issued to D. J. Remboski, et al. The diagnostic system in the aforesaid patent utilizes a pressure sensor mounted through the upper tank wall end a separate electrically operated flow regulation valve controls the flow of vapor to the engine during engine operation and for measuring the flow during the diagnostic test. The aforesaid diagnostic system employs a pressure sensor and an electrically operated flow control valve which are in addition to a separate electrically operated atmospheric vent valve controlling air flow into the vapor storage canister. In the aforesaid known fuel vapor emission control diagnostic system the pressure sensor and electrically operated valves are controlled by an electronic controller. This arrangement requires separate wiring to each of the valves and the sensor from the controller and thus increases the cost of assembly of the vehicle and complicates the assembly and creates additional sources of potential failure due to the complexity of routing separate wires around the tank at installation on the vehicle.
It has thus been desired to provide a way or means of on-board diagnostic testing of the fuel tank vapor emission control system in a manner which is simple, easy to install, low in cost and sufficiently robust to withstand continued exposure to the in service environment of the vehicle.
The present invention provides an electrically operated set of valves including a flow control orifice and differential pressure sensing transducer combined as a single unit in a common housing for use in controlling flow of fuel tank vapor emission to an engine air inlet and for use in on-board vehicle diagnostic testing for leakage in the vapor emission control system. The combination valve and pressure transducer assembly of the present invention includes electrical terminals for attachment of a single electrical connector thereto for simplifying the wiring harness in the vehicle and provides for a single location of mounting the valve assembly for connection to the fuel vapor storage canister and to the engine air inlet. The combination valve and pressure transducer of the present invention thus reduces the number of wires and hoses and simplifies installation. During engine operation one valve is opened to bypass a metering orifice across which the pressure transducer measures flow during leak testing under vacuum. The present invention thus combines the functions of fuel vapor flow control and diagnostic testing including flow measurement into a single unit which may be mounted remotely from the fuel tank. The combination valve and transducer assembly of the present invention utilizes a robust common housing for all of the components and provides for improved reliability and resistance to harsh environments encountered during vehicle service.